The present invention relates to a dynamic image correction method and dynamic image correction circuit of display device, wherein one frame is divided into a plurality of subfields (or subframes) on time-sharing basis and the subfields are made to emit light according to luminance levels of input signals for producing multi-gradation image.
Display devices incorporating PDP (Plasma Display Panel) and LCD (Liquid Crystal Display) are now attracting the attention of those who concerned as thin and lightweight display device. This drive method of the PDP is entirely different from that of conventional CRT in that the PDP is directly driven by input of digitized video signal. Thus, the luminance and gradation of the light emitted from panel surface are dependent on the number of bits of signal to be processed.
The PDP can be divided into two types, namely, AC-type and DC-types differing in basic characteristic. As for the AC-type PDP, sufficient characteristics can be obtained as to luminance and service life, while availability of only up to 64 gradations has been reported on trial manufacture basis, but a method for enabling 256 gradations by address display separation method in the future has already been proposed.
Drive sequence and drive waveform of the PDP to be used in this method, for example in the case of 8 bits and 256 gradations, are as shown in FIGS. 1(a) and (b) respectively.
In FIG. 1(a), one frame comprises 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8 having luminance ratios of 1, 2, 4, 8, 16, 32, 64, 128, and display of 256 gradations is available by Combining the luminances of 8 images.
In FIG. 1(b), each subfield comprises an address period for writing the data for 1 image and a sustain period for determining the luminance level of the subfield. During the address period, initial wall charge is formed simultaneously for each of the pixels of all the images, and then sustain pulse is given to all the images for display. The brightness of the subfield is proportional to the number of the sustain pulse and set to a predetermined luminance. The 256-gradation display is made available in this way.
When displaying a dynamic image by using an address display separation type display device as is described previously, input video signal (original signal) is a discrete signal, which is sampled for each frame (or field), thereby giving rise to a problem such as degradation of picture quality resulting from the visual disagreement in the direction of the movement of the dynamic image and the presence of the level not in accordance with the original signal. The dynamic image correction according to the prior art has been made by applying only one predetermined dynamic image correction method on the basis of the input video signal, regardless of the rate of the movement of block during one frame or during a plurality of frames. Here, one block means an area of image formed with one or a plurality of picture elements, e.g., 2xc3x972 picture elements.
According to the case of the prior art described above, however, the dynamic image is corrected by using only one same dynamic image correction method regardless of rapid moving part of dynamic image (hereinafter referred to as xe2x80x9crapid moving dynamic image partxe2x80x9d) and slow moving part of dynamic image (hereinafter referred to as xe2x80x9cslow moving dynamic image partxe2x80x9d), thereby causing a problem such that, when the dynamic image correction method is adapted for the rapid moving dynamic image part, correction for the slow moving dynamic image part becomes insufficient and vice versa.
The present invention, devised, in consideration of the problem of the prior art, for the display device having one frame divided into a plurality of subfields which emit light according to luminance level of input video signal for displaying multi-gradation image, is designed to provide a dynamic image correction method and a dynamic image correction circuit capable of effecting optimum dynamic image correction for both the rapid moving dynamic image part and the slow moving dynamic image part.
In the dynamic image correction method according to the present invention, for display device wherein one frame is divided into a plurality of subfields which emit light according to luminance level of input video signal for the display of multi-gradation image, the moving vector of the block during one frame or the blocks during a plurality of frames is or are detected, and, depending on whether the value of detected moving vector is larger than the preset value S or not, either a signal obtained by correcting input video signal by the rapid moving dynamic image correction means or a signal obtained by correcting input video signal by the slow moving dynamic image correction means is selectively output to the display device.
When the value of the moving vector detected on the basis of input video signal is larger than the preset value S, the input video signal is corrected by the rapid moving dynamic image correction means for output to the display device, while when the value of the detected moving vector is smaller than the preset value S, the input video signal is corrected by the slow moving dynamic image correction means for output to the display device, whereby an optimum dynamic image correction can be accomplished for both the rapid moving dynamic image part and slow moving dynamic image part to be displayed on the display device.
Further, according to the dynamic image correction method of the present invention, the rapid moving dynamic image correction means not only selects the light emitted from corresponding subfields among n number of subfields, SFn, SF(nxe2x88x921), . . . SF1, which constitute one frame, according to the luminance level of input video signal but also corrects the display positions of the n number of subfields SFnxcx9cSF1 in each frame of input video signal depending on the value of detected moving vector, while the slow moving dynamic image correction means selects the light emitted from the subfields SF(nxe2x88x921), . . . SF1 and SF1a, SF1a being adjacent to SF1 and having a luminance ratio equivalent to that of SF1, which constitute one frame, only when the luminance levels of input video signal has varied from 2(nxe2x88x921)xe2x88x921 to 2(nxe2x88x921), but selects the light emitted from the corresponding subfields among n number of subfields, SFnxcx9cSF1 not including the subfield SF1a with respect to the luminance levels other than those described previously. Therefore, when the value of detected moving vector is larger than the preset value S, the display positions of the subfields SFnxcx9cSF1 can be made to match with the visual path of the eye of a person watching the dynamic image. On the other hand, when the value of detected moving vector is smaller than the preset value S, the light emitted from the subfields, SF(nxe2x88x921)xcx9cSF1 and SF1a (e.g., SF3, SF2, SF1 and SF1a) is selected by the slow moving dynamic image correction means with respect to luminance level at 2(nxe2x88x921) (e.g., 8 when n=4) resulting when a luminance level has varied slightly from 2(nxe2x88x921)xe2x88x921 (e.g., 7) to a luminance level at 2(nxe2x88x921)(e.g., 8), thereby eliminating large variation of luminance.
The dynamic image correction circuit of present invention, incorporated into the display device wherein one frame is divided into a plurality of subfields on time-sharing basis for emitting light from the subfields according to luminance level of input video signal to display multi-gradation image, comprises a moving vector detector for detecting the moving vector of the block during one frame or moving vector of the block during a plurality of frames, a rapid moving dynamic image corrector for correcting for output an input video signal by using a proper dynamic image correction means when the value of the moving vector detected by the moving vector detector is larger than preset value S, a slow moving dynamic image corrector for correcting for output an input video signal by using a proper dynamic image correction means and a discriminating selector for discriminating an output signal from the rapid moving dynamic image corrector from an output signal from the slow moving dynamic image corrector for output to the display device depending on whether the value of the moving vector detected by the moving vector detector is larger or smaller than the preset value S. The discriminating selector outputs the input video signal corrected by the rapid moving dynamic image corrector to the display device when the value of detected moving vector is larger than the preset value S and outputs the input video signal corrected by the slow moving dynamic image corrector to the display device when the value of detected moving vector is smaller than the preset value S, so that an optimum dynamic image correction can be accomplished for both the rapid moving dynamic image part and the slow moving dynamic image part to be displayed on the display device.
The dynamic image correction circuit according to the present invention is designed so that the rapid moving dynamic image corrector not only selects the light emitted from corresponding subfields among n number of subfields SFnxcx9cSF1 constituting one frame and having luminance ratios 2(nxe2x88x921) through 20(=nxe2x88x92n) according to the luminance level of the input video signal but also corrects display positions of n number of subfields SFnxcx9cSF1 for each frame of input video signal depending on the value of moving vector detected by the moving vector detector, while the slow moving dynamic image corrector selects the light emitted from the subfields, SF(nxe2x88x921), . . . SF1, SF1a, constituting one frame and having luminance ratios 2(nxe2x88x921), 2(nxe2x88x922), . . . 20(=nxe2x88x92n), only when the luminance level of input video signal has varied from 2(nxe2x88x921)xe2x88x921 to 2(nxe2x88x921) and also selects the light emitted from corresponding subfields among n number of subfields, SFnxcx9cSF1, not including subfield SF1a, as to the luminance level other than those prescribed previously.
Therefore, when the value of detected moving vector is larger than the preset value S, the display positions of the subfields, SFnxcx9cSF1 can be made to match with the visual path of the eye of a person watching the dynamic image by using the rapid moving dynamic image corrector. On the other hand, when the value of detected moving vector is smaller than the preset value S, the light emitted from the subfields, SF(nxe2x88x921)xcx9cSF1 and SF1a (e.g., SF3, SF2, SF1 and SF1a) is selected by the slow moving dynamic image corrector with respect to the luminance level at 2(nxe2x88x921) resulting when the luminance level has slightly varied from a luminance level at 2(nxe2x88x921)xe2x88x921 (e.g., 7 when n=4) to 2(nxe2x88x921) (e.g., 8), thereby eliminating large variation of luminance.